It is known that the dusts entrained with the gases of a blast furnace and from a steel-making furnace contain a large part of the zinc introduced into the bath, e.g. in the form of galvanized scrap. The dusts are particularly rich in zinc when the melt in either furnace contains large proportions of galvanized-iron or galvanized-steel scrap.
It has already been proposed to recover the zinc in the form of its oxide from such dusts by extraction of the dusts from the gas by wet or dry separation. None of these techniques have proved to be commercially successful since the zinc content of the product is insufficiently high and the recovery itself is not satisfactory.
When the dusts are returned to the furnace they have a tendency to increase the zinc content of the melt and to cause problems in the iron or steel making process.
It is known, for example, that the presence of zinc in the fusion bed of a blast furnace causes difficulties in the operation thereof, not only because of an increased consumption of coke but also because of dangers to the personnel of the plant.
It is possible to reduce the problem by reducing the input of zinc to the furnace but this requires special methods in selecting the scrap or utilizing ores which are free from zinc or contain only minor quantities thereof.